全文获取类型
收费全文 | 2137篇 |
免费 | 90篇 |
国内免费 | 45篇 |
专业分类
化学 | 1572篇 |
晶体学 | 12篇 |
力学 | 92篇 |
数学 | 264篇 |
物理学 | 332篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 39篇 |
2021年 | 77篇 |
2020年 | 112篇 |
2019年 | 106篇 |
2018年 | 133篇 |
2017年 | 99篇 |
2016年 | 158篇 |
2015年 | 106篇 |
2014年 | 154篇 |
2013年 | 275篇 |
2012年 | 170篇 |
2011年 | 166篇 |
2010年 | 135篇 |
2009年 | 127篇 |
2008年 | 115篇 |
2007年 | 80篇 |
2006年 | 43篇 |
2005年 | 30篇 |
2004年 | 28篇 |
2003年 | 24篇 |
2002年 | 19篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有2272条查询结果,搜索用时 10 毫秒
41.
Seyed Hossein Hendi Fereshteh Azari Ebrahim Rahimi Mina Elahi Zahra Owjifard Zahra Armanfard 《Annalen der Physik》2020,532(10):2000162
It is known that scalar-tensor gravity models can be studied in Einstein and Jordan frames. In this paper, a model of scalar-tensor gravity in Einstein's frame is considered to calculate the Lifshitz-like black hole solutions with different horizon topologies. Thermodynamic properties and first order van der Waals-like phase transition are studied, and it is found that the Lifshitz parameter affects the phase structure. In addition, thermal stability is investigated by using the behavior of heat capacity and various methods of geometrical thermodynamics. 相似文献
42.
Saeed Khojaste Effatpanah Mohammad Hossein Ahmadi Seyed Hamid Delbari Giulio Lorenzini 《Entropy (Basel, Switzerland)》2022,24(2)
In recent decades, there has been an increasing trend toward the technical development of efficient energy system assessment tools owing to the growing energy demand and subsequent greenhouse gas emissions. Accordingly, in this paper, a comprehensive emergy-based exergoeconomic (emergoeconomic) method has been developed to study the biomass combustion waste heat recovery organic Rankine cycle (BCWHR-ORC), taking into account thermodynamics, economics, and sustainability aspects. To this end, the system was formulated in Engineering Equation Solver (EES) software, and then the exergy, exergoeconomic, and emergoeconomic analyses were conducted accordingly. The exergy analysis results revealed that the evaporator unit with 55.05 kilowatts and the turbine with 89.57% had the highest exergy destruction rate and exergy efficiency, respectively. Based on the exergoeconomic analysis, the cost per exergy unit , and the cost rate of the output power of the system were calculated to be 24.13 USD/GJ and 14.19 USD/h, respectively. Next, by applying the emergoeconomic approach, the monetary emergy content of the system components and the flows were calculated to evaluate the system’s sustainability. Accordingly, the turbine was found to have the highest monetary emergy rate of capital investment, equal to , and an output power monetary emergy of . Finally, a sensitivity analysis was performed to investigate the system’s overall performance characteristics from an exergoeconomic perspective, regarding the changes in the transformation coefficients (specific monetary emergy). 相似文献
43.
Kobra Mahdavipour Mahshid Khazaei Shadfar Hossein Rangani Jahromi Roberto Morandotti Rosario Lo Franco 《Entropy (Basel, Switzerland)》2022,24(3)
A witness of non-Markovianity based on the Hilbert–Schmidt speed (HSS), a special type of quantum statistical speed, has been recently introduced for low-dimensional quantum systems. Such a non-Markovianity witness is particularly useful, being easily computable since no diagonalization of the system density matrix is required. We investigate the sensitivity of this HSS-based witness to detect non-Markovianity in various high-dimensional and multipartite open quantum systems with finite Hilbert spaces. We find that the time behaviors of the HSS-based witness are always in agreement with those of quantum negativity or quantum correlation measure. These results show that the HSS-based witness is a faithful identifier of the memory effects appearing in the quantum evolution of a high-dimensional system with a finite Hilbert space. 相似文献
44.
Ghahraman Solookinejad Amir Sayid Hassan RozatianMohammad Hossein Habibi 《Applied Surface Science》2011,258(1):260-264
Zinc oxide (ZnO) thin film was fabricated by sol-gel spin coating method on glass substrate. X-ray reflectivity (XRR) and its optimization have been used for characterization and extracting physical parameters of the film. Genetic algorithm (GA) has been applied for this optimization process. The model independent information was needed to establish data analyzing process for X-ray reflectivity before optimization process. Independent information was exploited from Fourier transform of Fresnel reflectivity normalized X-ray reflectivity. This Fourier transformation (Auto Correlation Function) yields thickness of each coated layer on substrate. This information is a keynote for constructing optimization process. Specular X-ray reflectivity optimization yields structural parameters such as thickness, roughness of surface and interface and electron density profile of the film. Acceptable agreement exists between results obtained from Fourier transformation and X-ray reflectivity fitting. 相似文献
45.
46.
Esmaeili Hossein Armaghani T. Abedini A. Pop I. 《Journal of Thermal Analysis and Calorimetry》2019,135(6):3247-3257
Journal of Thermal Analysis and Calorimetry - The nanofluid is a mixture of base fluid and solid nanoparticles in nanosize. The heat transfer generated by the nanofluid is more than the base fluid... 相似文献
47.
Sorayya Ghasemi JokoPriyanto Wibowo Hossein Amini-khoei 《Natural product research》2019,33(12):1828-1831
For more effectiveness and overcoming the drug resistance Chemotherapy agents, the combination treatment is raised. Flavonoids with different anti-cancer effects are an appropriate choice as lead compounds. Over expressed MiR-21 in prostate cancer is associated with metastasis and drug resistance to chemotherapy with Docetaxel. In this study, the anticancer effect of 4′, 5, 7-Trihydroxy-3′, 5′-dimethoxyflavone (Tricin) was investigated with Docetaxel on PC3 cell line. Tricin was initially isolated from the Allium atroviolaceum by column chromatography and recrystallization method. The chemical structure of isolate was elucidated by spectroscopic techniques. IC50 of Tricin and Docetaxel were assessed 117.5 ± 4.4 μM and 0.1 ± 0.02 nM by MTT assay, respectively. Analysis of results indicates the synergistic effect of combination therapy on decreased proliferation. MiR-21 in treated cells with Tricin significantly decreased compared to control cells. So, Tricin can be effective in the reduction of metastasis and drug resistance of Docetaxel. 相似文献
48.
Russian Journal of Electrochemistry - The use of hematite as a photoanode has been limited due to its optoelectronic properties and a large overpotential for photo-assisted water splitting. In this... 相似文献
49.
Chromene substructure is an important structural motif present in a variety of medicines, natural products, and materials showing biological activities. Here, a simple and convenient procedure for the synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives is described. For this purpose, Fe3O4 nanoparticles supported on β-cyclodextrin-guanidine were successfully prepared and used as catalyst. The structure of this catalyst was assigned by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and vibrating sample magnetometer techniques. The prepared nanocomposites were used as a highly active, heterogeneous, and reusable nanocatalyst for the one-pot, three-component reaction of 4-hydroxycoumarin, aromatic aldehydes, and ethyl cyanoacetate. This method has advantages such as mild conditions, high yields, easy workup and simple purification of products, little catalyst loading, cost efficiency, and reusability of the catalyst. 相似文献
50.
Nickel Schiff-base complex immobilized on silica-coated Fe3O4 as a heterogeneous catalyst was designed and characterized by different techniques, such as Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma (ICP) and vibrating sample magnetometry (VSM) thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET). The synthesized nanocatalyst has been explored as a new and efficient recyclable heterogeneous catalyst for the one-pot three-component synthesis of tetrahydrobenzo[b]pyran derivatives. The reaction proceeds smoothly to supply the respective products in excellent yields and low reaction times. The catalyst can be easily recovered by a magnetic field and reused for eight consecutive reaction cycles without significant loss of activity. 相似文献